1. Field of the Invention
This invention relates to a preferably cylindrical piezoelectric transducer and a preferably cylindrical piezoelectric vibrating element preferably used as a vibrating element in the cylindrical piezoelectric transducer. The preferably cylindrical piezoelectric vibrating element includes a preferably cylindrical piezoelectric polymer membrane.
2. Description of the Prior Art
Piezoelectric polymer membranes are well-known, being described in Japanese patent publications JP-58060584-A and JP-08036917-A.
One known and commercially available electroacoustic transducer has a cylindrical vibrating element including a cylindrical piezoelectric polymer membrane formed by overlapping and connecting both edges of a tape of the piezoelectric polymer membrane in the width-wise direction. A pair of electrodes is provided on the outer and inner surfaces of the cylindrical piezoelectric polymer membrane, with the membrane providing an electrical connection between the electrodes. The cylindrical vibrating element is mounted around a columnar holder, with a very small gap between the element and the peripheral surface of the holder.
Such a commercially available transducer is used for transmitting and receiving ultrasonic waves and exhibits reasonably good transmitting and receiving performance over relatively short distances. However, such transducers do not exhibit sufficient sensitivity when used for transmitting and receiving over relatively long distances. Furthermore, sensitivity varies and is not uniform about the periphery of the cylindrical vibrating element.
Recently, transducers having such cylindrical vibrating elements have been tried in applications requiring uniform ultrasound output around the circumference of the cylindrical vibrating element. These conventional cylindrical vibrating elements exhibit large variations in ultrasound output around the circumference of the vibrating element, which is unsatisfactory.
An object of this invention is to address the above-described problems of conventional transducers with vibrating elements by providing a cylindrical piezoelectric transducer having an enhanced range of useful applications in comparison comparing to conventional transducers, thus satisfy the needs detailed above.
These objectives of the invention are accomplished by providing a cylindrical piezoelectric transducer having a cylindrical piezoelectric vibrating element embracing the structures as set forth below.
In accordance with one aspect of the invention a cylindrical piezoelectric transducer comprises a columnar holder, a vibrating element comprising at least one cylindrical piezoelectric polymer membrane provided around the holder with clearance between an inner peripheral surface of the vibrating element and an outer peripheral surface of the holder, with a peripheral fixing portion being provided at one peripheral end portion of the vibrating element to secure the vibrating element to the holder.
A cylindrical piezoelectric vibrating element according to the present invention comprises a cylindrical piezoelectric polymer membrane comprising a joined portion, formed by abutting both transversely extending edges which define longitudinal extremities of the piezoelectric polymer membrane and joining the edges with tape in the width-wise direction.
In one embodiment of the cylindrical piezoelectric transducer according to this invention, it is preferable that the fixing portion comprises a protruding portion formed along the periphery of the holder and an adhesive layer provided on the protruding portion. It is also preferable in accordance with another embodiment of the invention that the fixing portion comprises a protruding portion formed along the periphery of the holder and a fixing ring positioned on the protruding portion supporting the vibrating element. Further it is preferable in accordance with yet another embodiment of the invention that the fixing portion have a tapered or canted surface at the outer surface of the protruding portion with a taper angle of the tapered or canted surface preferably being in the range of from about 5 degrees to about 30 degrees.
In the cylindrical piezoelectric polymer membrane vibrating element according to the invention, it is preferable that the joined portion have adhesive tape having a predetermined length pasted on the outer surface and/or the inner surface of the piezoelectric polymer membrane vibrating element. Further it is preferable that the relation of JL/PLxe2x89xa60.25 is satisfied, where JL is the predetermined length of the adhesive tape and PL is the circumference of the piezoelectric polymer membrane.